Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $168.42   13.204%   $190.6582   $190.66   $190.65   $190.70  
  Purchase #2 $207.41   11.425%   $231.1066   $231.11   $231.10   $231.10  
  Purchase #3 $41.78   9.296%   $45.6639   $45.66   $45.65   $45.70  
  Purchase #4 $65.25   12.351%   $73.309   $73.31   $73.30   $73.30  
  Purchase #5 $246.50   3.228%   $254.457   $254.46   $254.45   $254.50  
  Purchase #6 $54.37   11.387%   $60.5611   $60.56   $60.55   $60.60  
  Purchase #7 $170.58   13.637%   $193.842   $193.84   $193.85   $193.80  
  7 purchase totals = $954.31       $1,049.5978   $1,049.60   $1,049.55   $1,049.70